This invention relates generally to data storage systems, and more particularly to data storage systems having redundancy arrangements to protect against total system failure in the event of a failure in a component or subassembly of the storage system.
As is known in the art, large mainframe, or host, computer systems require large capacity data storage systems. These large mainframe, or host computer systems generally include data processors, which perform many operations on data introduced to the computer system through peripherals including the data storage system. The results of these operations are output to peripherals, including the storage system.
One type of data storage system is a magnetic disk storage system. Here, a bank of disk drives and the mainframe, or host computer system are coupled together through a system interface. The system interface includes Central Processing Unit (CPU), or xe2x80x9cfront endxe2x80x9d, controllers (or directors) and xe2x80x9cback endxe2x80x9d disk controllers (or directors). The system interface operates the controllers (or directors) in such a way that they are transparent to the computer. That is, data is stored in, and retrieved from, the bank of disk drives in such a way that the mainframe, or host computer system merely thinks it is operating with one mainframe, or host memory. One such system is described in U.S. Pat. No. 5,206,939, entitled xe2x80x9cSystem and Method for Disk Mapping and Data Retrievalxe2x80x9d, inventors Moshe Yanai, Natan Vishlitzky, Bruno Alterescu and Daniel Castel, issued Apr. 27, 1993, and assigned to the same assignee as the present invention.
As described in such U.S. patent, the system interface may also include, in addition to the CPU controllers (or directors) and disk controllers (or directors), addressable cache memories. The cache memory is a semiconductor memory and is provided to rapidly store data from the mainframe computer system before storage in the disk drives, and, on the other hand, store data from the disk drives prior to being sent to the mainframe computer. The cache memory being a semiconductor memory, as distinguished from a magnetic memory as in the case of the disk drives, is much faster than the disk drives in reading and writing data.
The CPU controllers, disk controllers and cache memory are interconnected through a backplane printed circuit board. More particularly, disk controllers are mounted on disk controller printed circuit boards. CPU controllers are mounted on CPU controller printed circuit boards. And, cache memories are mounted on cache memory printed circuit boards. The disk controller, CPU controller and cache memory printed circuit boards plug into the backplane printed circuit board. In order to provide data integrity in case of a failure in a controller, the backplane printed circuit board has one, or more, pairs of buses. One section of the disk controllers is connected to one or more of the buses and another section of the disk controllers is connected to one or more of the other buses. Likewise, one set of the CPU controllers is connected to one or more of the buses and another set of the CPU controllers is connected to one or more of the other buses. The cache memories are connected to all of the buses. Each one of the buses provides data, address and control information.
Thus, the use of two, or more, buses provides a degree of redundancy to protect against a total system failure in the event that the controllers, or disk drives connected to one bus fail. Further, the use of two, or more, buses increases the data transfer bandwidth of the system compared to a system having a single bus.
As is also known in the art, one type of system interface includes a backplane having directors plugged into one surface of the backplane and Input/Output (I/O) adapters plugged into an opposite surface of the backplane. The backplane is a printed circuit board used to properly interconnect the directors and the I/O adapters. One portion of the I/O adapters is connected by cables to the host computer and another portion are connected to the disk drives. In some systems Small Computer Signal Interface (SCSI) data busses are used in the cables to transfer data through the system interface (from I/O adapters plugged into the backplane) to the bank of disk drives. One type of SCSI bus is a single-ended SCSI data bus. Such single-ended SCSI bus is typically in a cable having a grounded conductor and a single conductor. Another type of SCSI data bus is a differential SCSI bus, e.g., Low Voltage Differential (LVD) SCSI. Such differential SCSI data buses have a pair of conductors within the cable. While the differential SCSI bus offers the advantage of greater isolation from external noise and is able to carry data faster than single-ended SCSI data buses, the differential SCSI bus requires twice as may connector pins as the single-ended SCSI data bus thereby making its use limited to backplanes which can accommodate the extra connector pins.
In accordance with the present invention, a system is provided for coupling data between a host computer and a bank of disk drives. The system includes a plurality of directors for controlling the flow of the data between host computer and the bank of disk drives. Each one of the directors has a primary port and a secondary port. The system includes a first I/O section coupled to a first one of a pair of disk drive sections in the bank of disk drives and a second I/O section coupled to a second one of the pair of disk drive sections in the bank of disk drives. A backplane is provided for electrically interconnecting: the primary port of a first one of a pair of the directors to the first I/O section through a first differential data bus; the secondary port of the first one of the pair of directors to the second I/O section through a first single-ended data bus; the primary port of a second one of the pair of directors to the second I/O section through a second differential data bus; and, the secondary port of the second one of the pair of directors to the first I/O section through a second single-ended data bus. Each one of the first and second I/O sections includes a single-ended/differential data bus converter. The converter of the first I/O section is coupled between the second single-ended data bus and the first differential data bus and the converter of the second I/O section is coupled between the first single-ended data bus and the second differential data bus.
In one embodiment, each one of the directors in the pair thereof includes a processor for, during a normal operating mode, coupling data between such processor and a corresponding one of the pair of disk drive sections through a corresponding one of the first and second differential buses. In the event of a fault in the first one of the pair of directors, data is coupled between the second one of the pair of directors and the first one of the pair of disk drive sections through: the second single-ended data bus; a first one of the pair of single-ended/differential data bus converters; and the first differential data bus. Further, during the fault, data continues to be coupled between the second one of the pair of directors and the second one of the disk drive sections through the second differential data bus.
With such an arrangement, the number of connector pins required at the backplane is reduced while still enabling differential SCSI data transfers between the host computer and the bank of disk drives during the normal operating mode. However, in the event of a failure of one of a pair of directors, enabling differential SCSI data to be transferred between the backplane and the bank of disk drives with single-ended SCSI data being transferred only through the shorter, more isolated backplane only when the secondary bus is activated.
In one embodiment of the invention, a data storage system is provided having a host computer; a bank of disk drives comprising a plurality of disk drive sections; and a system interface for coupling data between the host computer and the bank of disk drives. The system interface includes a backplane; a plurality of directors connected to front side connectors of the backplane; and an I/O interface connected to rear side connectors of the backplane. The directors are adapted to control the flow of the data between host computer and the bank of disk drives. Each one of the directors has a primary port and a secondary port connected to the front side connectors of the backplane. The I/O interface has a first section and a second section. The first section of the I/O interface is coupled to a first one of a pair of disk drive sections and the second section of the I/O interface is coupled to a second one of the pair of disk drive sections. The backplane electrically interconnects: the primary port of a first one of a pair of the directors to the first section of the I/O interface through a first differential SCSI data bus; the secondary port of the first one of the pair of directors to the second section of the I/O interface through a first single-ended SCSI data bus; the primary port of a second one of the pair of directors to the second section of the I/O interface through a second differential SCSI data bus; and, the secondary port of the second one of the pair of directors to the first section of the I/O interface through a second single-ended SCSI data bus. Each one of the first and second sections of the I/O interface includes a single-ended/differential SCSI data bus converter. The converter of the first section of the I/O interface is coupled between the second single-ended SCSI data bus and the first differential SCSI data bus. The converter of the second section of the I/O interface is coupled between the first single-ended SCSI data bus and the second differential SCSI data bus. In one embodiment, a system interface is provided for coupling data between a host computer and a bank of disk drives. The interface includes: a backplane; a plurality of directors connected to one side of the backplane; and an I/O interface connected to an opposite side of the backplane. The directors are adapted to control the flow of the data between host computer and the bank of disk drives. Each one of the directors has a primary port and a secondary port connected to the front side of the backplane. The I/O interface has a first section coupled to the first one of the pair of disk drive sections and a second section coupled to the second one of the pair of disk drive sections. The backplane electrically interconnects: the primary port of a first one of a pair of the directors to the first section of the I/O interface through a first differential SCSI data bus; the secondary port of the first one of the pair of directors to the second section of the I/O interface through a first single-ended SCSI data bus; the primary port of a second one of the pair of directors to the second section of the I/O interface through a second differential SCSI data bus; and, the secondary port of the second one of the pair of directors to the first section of the I/O interface through a second single-ended SCSI data bus. Each one of the first and second sections of the I/O interface includes a single-ended/differential SCSI data bus converter, the converter of the first section of the I/O interface being coupled between the second single ended SCSI data bus and the first differential SCSI data bus and the converter of the second section of the I/O interface being coupled between the first single ended SCSI data bus and the second differential SCSI data bus.